From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E5BDC198A29 for ; Sat, 12 Apr 2025 06:03:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744437797; cv=none; b=ky9cdzTxev65YSKTRTGNV9eR0E8yQP61AGDiGJ0tttskJjAinmeO9hDQPv/HKuF7JIq08dh+OtQSPsVOSRxyqM5WHrKYbmE6L+MsHJmD0VOEOHnpE/8iT3mqdTQbBLq+0gL8ovPqPuyrz/VGmYV9lPqbTuHnw4+JYIm9a1U40Mk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744437797; c=relaxed/simple; bh=P4LjumHh/z+dK8+rRpiX4HsoiipXYY7JIUy+sWGN32s=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=KYfbWlvKbtQx5oyBZnAdWkn/POFZ/PbeJE2khPIhdTA5xcrjm1PQEj45AVv1ndBmsVc0EKiVeymoDwljyxN9UpU6objJaCWnMHOr05khjcVVKskc4KaYQAKCMnaj1W3NKrQufj8YRpgb6wT1nsFvIetAjAod5vdYHINQfAkXiJo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=OHecZFDv; arc=none smtp.client-ip=209.85.214.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="OHecZFDv" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-224347aef79so35160975ad.2 for ; Fri, 11 Apr 2025 23:03:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1744437794; x=1745042594; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=naVwflgBNbBg0NLcXqLDTTYAuw4Vp+VwbWUapN6oLCc=; b=OHecZFDvYHB+JWpM9vd7LmmKUVKRaQFOJ4wVggTG2CPlxxx121OMLUZ9JmbUOYOHrB 7Op6l1s44YHA39VRI0iNaSi3TDlYkztfR4XFoj7vmYHdzI6BTptcBFvuhUEHKP3Y+wh6 cIU3vyFeCMP5okwvrZ9WbI9NMPWo8gWfqknSpkepsH2J052n836ub8VpkYqw+wiYQRqH 7bQbnsgahRazACuwZe5vcxOGqIq+guImaG4uhZSXlU9kU1si17J9hsSS369R9vFitG8x Hy4yg25mBAr+E7NCprCtYKlDHKMaSNAdYu9P2GVs052RRJOIPBBX0tbAD7ImHdzj0dQI VeKw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1744437794; x=1745042594; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=naVwflgBNbBg0NLcXqLDTTYAuw4Vp+VwbWUapN6oLCc=; b=bRInXMUdo3fwEDxAl54O4Vp84k7P9niYDIPEqaBS+VdKG8sL5mPjjH4HvFtkY4BrVY mW1a6bmRAQ5uuSjJQDeunv5mQiznXrvry5c3rLCnXJ+9SWRSwhuMO0vFZL2RWpVMsi3r 8JLmKCTF7m8vBVv+hLxRlTKo/SK8IHTk+vrqutzBuEdF52kgkjdS1Kblfd2C3FDQ696O nT6CgYVMMWC3ykf5Y+7+mTISiuGIlM+jzL53BsxQLEte0Lzt5UdjUytK+7Bby+kRkJqS bcb1ss22QjUWUctj5ZgKDJ8hMPeRfDcbJqXzMkX4plGsj53KTXqqT1108LEsBXkWnGG4 7j6A== X-Gm-Message-State: AOJu0YzMv4YTZENs4Vu6LdRYE+AnpZMN0jOhXocUgay1xDoToB3KrnAD cXuCY5KJDA4n8QHKDg6BdNcprg0eWdHKUU6fOhpK8ZsM4OyxJVyABgOmYfTOvKTcfVyBjm2pFn2 3mjFQdhKDPNK3NxG8nhjv4dZzD6nibQVqRumQF16s5cflXnLyLqzPIWcnIA9nIsTvrugj4vjLb7 YwsGFsff2SPTSEqVoMTsuKlpNYR09MkuNJ6wRCGz2d9Olu X-Google-Smtp-Source: AGHT+IEf7DGwnkqpsVBaZ9GPliFq+nyLl/3/Hol8NZMDKrMj8xAjm65Lqq8cIUhdrpcFACwmNxOWRDODIi6y X-Received: from pjbsi10.prod.google.com ([2002:a17:90b:528a:b0:2ef:7af4:5e8e]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:1b27:b0:223:f408:c3dc with SMTP id d9443c01a7336-22bea4952f7mr71861345ad.9.1744437794244; Fri, 11 Apr 2025 23:03:14 -0700 (PDT) Date: Fri, 11 Apr 2025 23:02:39 -0700 In-Reply-To: <20250412060258.3844594-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250412060258.3844594-1-jstultz@google.com> X-Mailer: git-send-email 2.49.0.604.gff1f9ca942-goog Message-ID: <20250412060258.3844594-6-jstultz@google.com> Subject: [PATCH v16 5/7] sched: Add an initial sketch of the find_proxy_task() function From: John Stultz To: LKML Cc: John Stultz , Joel Fernandes , Qais Yousef , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Steven Rostedt , Ben Segall , Zimuzo Ezeozue , Mel Gorman , Will Deacon , Waiman Long , Boqun Feng , "Paul E. McKenney" , Metin Kaya , Xuewen Yan , K Prateek Nayak , Thomas Gleixner , Daniel Lezcano , Suleiman Souhlal , kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Add a find_proxy_task() function which doesn't do much. When we select a blocked task to run, we will just deactivate it and pick again. The exception being if it has become unblocked after find_proxy_task() was called. Greatly simplified from patch by: Peter Zijlstra (Intel) Juri Lelli Valentin Schneider Connor O'Brien Cc: Joel Fernandes Cc: Qais Yousef Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Valentin Schneider Cc: Steven Rostedt Cc: Ben Segall Cc: Zimuzo Ezeozue Cc: Mel Gorman Cc: Will Deacon Cc: Waiman Long Cc: Boqun Feng Cc: "Paul E. McKenney" Cc: Metin Kaya Cc: Xuewen Yan Cc: K Prateek Nayak Cc: Thomas Gleixner Cc: Daniel Lezcano Cc: Suleiman Souhlal Cc: kernel-team@android.com [jstultz: Split out from larger proxy patch and simplified for review and testing.] Signed-off-by: John Stultz --- v5: * Split out from larger proxy patch v7: * Fixed unused function arguments, spelling nits, and tweaks for clarity, pointed out by Metin Kaya * Fix build warning Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202311081028.yDLmCWgr-lkp@intel.com/ v8: * Fixed case where we might return a blocked task from find_proxy_task() * Continued tweaks to handle avoiding returning blocked tasks v9: * Add zap_balance_callbacks helper to unwind balance_callbacks when we will re-call pick_next_task() again. * Add extra comment suggested by Metin * Typo fixes from Metin * Moved adding proxy_resched_idle earlier in the series, as suggested by Metin * Fix to call proxy_resched_idle() *prior* to deactivating next, to avoid crashes caused by stale references to next * s/PROXY/SCHED_PROXY_EXEC/ as suggested by Metin * Number of tweaks and cleanups suggested by Metin * Simplify proxy_deactivate as suggested by Metin v11: * Tweaks for earlier simplification in try_to_deactivate_task v13: * Rename rename "next" to "donor" in find_proxy_task() for clarity * Similarly use "donor" instead of next in proxy_deactivate * Refactor/simplify proxy_resched_idle * Moved up a needed fix from later in the series v15: * Tweaked some comments to better explain the initial sketch of find_proxy_task(), suggested by Qais * Build fixes for !CONFIG_SMP * Slight rework for blocked_on_state being added later in the series. * Move the zap_balance_callbacks to later in the patch series v16: * Move the enqueue_task_rt() out to later in the series, as suggested by K Prateek Nayak * Fixup whitespace error pointed out by K Prateek Nayak * Use put_prev_set_next_task as suggested by K Prateek Nayak * Try to rework find_proxy_task() locking to use guard and proxy_deactivate_task() in the way Peter suggested. --- kernel/sched/core.c | 100 +++++++++++++++++++++++++++++++++++++++++-- kernel/sched/sched.h | 10 ++++- 2 files changed, 106 insertions(+), 4 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 82817650a635b..88acb47f50d0f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6600,7 +6600,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) * Otherwise marks the task's __state as RUNNING */ static bool try_to_block_task(struct rq *rq, struct task_struct *p, - unsigned long task_state) + unsigned long task_state, bool deactivate_cond) { int flags = DEQUEUE_NOCLOCK; @@ -6609,6 +6609,9 @@ static bool try_to_block_task(struct rq *rq, struct task_struct *p, return false; } + if (!deactivate_cond) + return false; + p->sched_contributes_to_load = (task_state & TASK_UNINTERRUPTIBLE) && !(task_state & TASK_NOLOAD) && @@ -6632,6 +6635,90 @@ static bool try_to_block_task(struct rq *rq, struct task_struct *p, return true; } +#ifdef CONFIG_SCHED_PROXY_EXEC +static inline struct task_struct *proxy_resched_idle(struct rq *rq) +{ + put_prev_set_next_task(rq, rq->donor, rq->idle); + rq_set_donor(rq, rq->idle); + set_tsk_need_resched(rq->idle); + return rq->idle; +} + +static bool __proxy_deactivate(struct rq *rq, struct task_struct *donor) +{ + unsigned long state = READ_ONCE(donor->__state); + + /* Don't deactivate if the state has been changed to TASK_RUNNING */ + if (state == TASK_RUNNING) + return false; + /* + * Because we got donor from pick_next_task, it is *crucial* + * that we call proxy_resched_idle before we deactivate it. + * As once we deactivate donor, donor->on_rq is set to zero, + * which allows ttwu to immediately try to wake the task on + * another rq. So we cannot use *any* references to donor + * after that point. So things like cfs_rq->curr or rq->donor + * need to be changed from next *before* we deactivate. + */ + proxy_resched_idle(rq); + return try_to_block_task(rq, donor, state, true); +} + +static struct task_struct *proxy_deactivate(struct rq *rq, struct task_struct *donor) +{ + if (!__proxy_deactivate(rq, donor)) { + /* + * XXX: For now, if deactivation failed, set donor + * as unblocked, as we aren't doing proxy-migrations + * yet (more logic will be needed then). + */ + donor->blocked_on = NULL; + } + return NULL; +} + +/* + * Initial simple sketch that just deactivates the blocked task + * chosen by pick_next_task() so we can then pick something that + * isn't blocked. + */ +static struct task_struct * +find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf) +{ + struct task_struct *p = donor; + struct mutex *mutex; + + mutex = p->blocked_on; + /* Something changed in the chain, so pick again */ + if (!mutex) + return NULL; + /* + * By taking mutex->wait_lock we hold off concurrent mutex_unlock() + * and ensure @owner sticks around. + */ + guard(raw_spinlock)(&mutex->wait_lock); + + /* Check again that p is blocked with blocked_lock held */ + if (!task_is_blocked(p) || mutex != __get_task_blocked_on(p)) { + /* + * Something changed in the blocked_on chain and + * we don't know if only at this level. So, let's + * just bail out completely and let __schedule + * figure things out (pick_again loop). + */ + return NULL; /* do pick_next_task again */ + } + return proxy_deactivate(rq, donor); +} +#else /* SCHED_PROXY_EXEC */ +static struct task_struct * +find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf) +{ + WARN_ONCE(1, "This should never be called in the !SCHED_PROXY_EXEC case\n"); + return donor; +} +#endif /* SCHED_PROXY_EXEC */ + /* * __schedule() is the main scheduler function. * @@ -6742,12 +6829,19 @@ static void __sched notrace __schedule(int sched_mode) goto picked; } } else if (!preempt && prev_state) { - try_to_block_task(rq, prev, prev_state); + try_to_block_task(rq, prev, prev_state, + !task_is_blocked(prev)); switch_count = &prev->nvcsw; } - next = pick_next_task(rq, prev, &rf); +pick_again: + next = pick_next_task(rq, rq->donor, &rf); rq_set_donor(rq, next); + if (unlikely(task_is_blocked(next))) { + next = find_proxy_task(rq, next, &rf); + if (!next) + goto pick_again; + } picked: clear_tsk_need_resched(prev); clear_preempt_need_resched(); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 154f0aa0c6322..ea2c987005bc1 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2264,6 +2264,14 @@ static inline int task_current_donor(struct rq *rq, struct task_struct *p) return rq->donor == p; } +static inline bool task_is_blocked(struct task_struct *p) +{ + if (!sched_proxy_exec()) + return false; + + return !!p->blocked_on; +} + static inline int task_on_cpu(struct rq *rq, struct task_struct *p) { #ifdef CONFIG_SMP @@ -2473,7 +2481,7 @@ static inline void put_prev_set_next_task(struct rq *rq, struct task_struct *prev, struct task_struct *next) { - WARN_ON_ONCE(rq->curr != prev); + WARN_ON_ONCE(rq->donor != prev); __put_prev_set_next_dl_server(rq, prev, next); -- 2.49.0.604.gff1f9ca942-goog